1. Field of the Invention
Pneumatic apparatus for monitoring the conditions of a drilling fluid circulating system of a well.
2. Description of the Prior Art
It is customary in well drilling operations, as for example oil and gas wells, to utilize a drilling fluid to remove cuttings and to maintain proper bottom-hole pressures and temperatures. In a typical operation, the drilling fluid, commonly called drilling mud, is circulated from mud tanks located on the surface and adjacent the drilling rig down the drill pipe, out the rotary bit, and returned to the mud tanks through the annulus formed between the bore hole and the drill pipe. Since the drilling mud is continually being circulated from the bottom of the well, it is used as a source of information as to the nature of the various strata or formations which are pierced by the drill bit. The materials contained in the mud and the back pressure exerted by it tell the operator if certain formations may be productive of hydrocarbons, and the pressure contained in the formations. Thus, it is important to closely monitor pressure and flow rate of the circulating system as the well is being drilled.
Various problems often arise during drilling operations which may damage the well circulating system, the formations, surface property, or cause erroneous information to be obtained. One of these problems is known as a washout which occurs when a hole develops in the drill pipe. A portion of the drilling mud then passes through this hole and up the annulus rather than being circulated down to the bit. The mud passing through the hole often severs the drill pipe leading to an expensive fishing operation. The formation surrounding the hole is often damaged or washed away by the escaping mud. Since a portion of the mud is short-circuiting the system, a decrease in drill pipe pressure, the pressure required to circulate the mud through the well, will be an indication that a washout has occurred.
Another problem that occurs during drilling operations is lost circulation, a condition where mud flow into the well exceeds mud flow from the well. This may occur when an abnormally low-pressure zone is encountered and the drilling pressure, which had been needed for proper drilling through to upper zones, exceeds the pressure of the formation currently being drilled. In this situation, mud may be forced out into the low pressure formation with the upper high pressure formations flowing into the borehole. This situation can lead to lost control of the well resulting in a blowout. The formation may be severely damaged and possibly prevent any future hydrocarbon production from it. Also, significant amounts of expensive drilling mud may be lost.
As is apparent, it is important that an operator continually monitor the conditions of the circulating system in order to prevent these and other problems which exist during drilling operations.
Currently, several monitoring devices are utilized in the oil drilling industry. Many of these instruments are partially or totally electrically operated. Due to the hazardous environment in which drilling operations are conducted, electrically operated equipment can present severe problems and limitations. Also, the corrosive atmosphere of offshore operations limits the use of electrical systems.
There are currently pneumatic instruments which measure one variable or another in a circulating system, but no system currently available conveniently presents a representative picture of the circulating system in a manner which enables the operator to quickly diagnose the problem and remedy the situation.